Image forming apparatus

ABSTRACT

An image forming apparatus of the present invention intends to reduce a difference of usage frequency among a plurality of sheet feeding section and comprises: a plurality of sheet feeding section capable of feeding different types of sheets; a printer main body for forming an image on a sheet fed by the sheet feeding section; an accumulation counter for counting the accumulation quantity of fed sheets of each of the plural sheet feeding section; and a controller for determining bias of usage frequency of each sheet feeding section based on a counting result of the accumulation counter and changing the allocation of the sheets of each sheet feeding section to reduce the bias of the usage frequency of each sheet feeding section.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus having a plurality of sheet feeding sections.

2. Description of the Related Art

Generally, the image forming apparatus such as a copier and printer is provided with a plurality of feeding trays. Different kinds of sheets are often set in these feeding trays depending on user's usage purpose. In the meantime, the “different kinds” means that at least one of various parameters for specifying the sheet, such as its material, thickness, size is different.

When a print job is received, the controller of the image forming apparatus selects a feeding tray in which sheets of material and thickness specified by user are accommodated or a feeding tray in which sheets of a size suitable for the size of image to be formed are accommodated and starts image forming operation.

Generally, when different kinds of sheets are set in a plurality of the feeding trays, a difference in frequency of usage occurs depending on sheets used usually or sheets used rarely. In an ordinary office environment, the usage frequency of plain paper or thick paper of A3 size or B4 size is low although its demand exists while the plain paper of A4 size or B5 size is used frequently. when the difference of the usage frequency is accumulated, a large bias is generated in the accumulation quantities of fed sheets among the feeding trays.

An ordinary feeding apparatus conveys and separates the sheets using a rubber roller or rubber pad. These members are worn and deteriorated as the quantity of sheets increases and their surfaces are deteriorated when they are left in an unused state for a long time. when this deterioration progresses, the friction coefficient of a contact face with the sheet drops or the conveyance amount drops due to wearing of the outer periphery of the roller, so that a jam due to a conveyance delay or double feeding occurs. This state is called fulfilled service life of the feeding roller or separating pad.

When there exists a bias in the usage frequency among the feeding trays as described above, rollers of the feeding trays used frequently are worn unevenly or the rollers of the feeding tray used less frequently are deteriorated because they are left not used, so that the service life is fulfilled early. As a consequence, such a trouble as jamming and double feeding is likely to occur. Further, there occurs such a problem that a service person needs to replace the feeding rollers frequently. To eliminate these problems, the usage frequency of the feeding tray needs to be equalized.

Then, the method described in Japanese Patent Application Laid-Open No. 2002-255380 has been proposed conventionally as case where sheets of the same size and same kind are set in a plurality of feeding trays.

That is, this feeding portion including a plurality of sheet storage portions for accommodating sheets of the same size and material is provided with a selecting means for selecting a sheet storage portion from which sheets are to be fed, in order to equalize the accumulation feeding frequency of each sheet storage portion.

However, the above-described conventional technology is premised on that sheets of the same size and kind are set in the plurality of the feeding trays. Thus, that conventional technology cannot be applied to an ordinary use condition in which sheets of different kinds are set in each feeding tray.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide an image forming apparatus capable of reducing a difference in the usage frequency among the plurality of the sheet feeding sections.

To achieve above-mentioned object, the present invention provides an image forming apparatus comprising:

a plurality of sheet feeding sections capable of feeding different types of sheets;

an image forming portion which forms an image on a sheet fed by the sheet feeding sections;

an accumulation feeding quantity counting means for counting the accumulation quantity of fed sheets of each of the plural sheet feeding sections; and

a control means which determines the bias of usage frequency of each sheet feeding sections based on a counting result of the accumulation feeding quantity counting means and changes the allocation of the sheets of each sheet feeding sections to reduce the bias of the usage frequency of each sheet feeding sections.

The present invention can reduce the difference in the usage frequency among the plurality of the sheet feeding sections.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with further advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a flow chart showing an example of frequency equalizing processing of the embodiment of the present invention;

FIG. 2 is a diagram showing an example of the profile of each feeding tray of the present invention;

FIG. 3 is a diagram showing an example of the profile after the kinds of sheets used in each feeding tray of the invention are reallocated;

FIG. 4 is a diagram showing an example of the profile of each feeding tray of the invention;

FIG. 5 is a diagram showing an example of the profile after the kinds of sheets used in each feeding tray of the invention are reallocated;

FIG. 6 is a schematic sectional view of an image forming apparatus of the embodiment of the present invention; and

FIG. 7 is a block diagram of a control portion of the embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the accompanying drawings and embodiments. However, the dimension, material, shape, relative arrangement and the like of components described in the embodiments do not restrict the invention to only those unless specified otherwise. The material, shape and the like of members described in a following description are the same as in description of background art unless specified otherwise.

(Image Forming Apparatus)

An example of the image forming apparatus which can adopt the present invention preferably will be described with reference to FIG. 6. FIG. 6 shows the image forming apparatus according to an embodiment of the present invention.

An image forming apparatus 100 comprises a printer main body 1 for forming an image on a sheet and a reading portion 2 for a case where it is made to function as a copier. Although this embodiment will be described about a copier type image forming apparatus having the reading portion, the present invention may be applied to a printer type image forming apparatus having no reading portion.

A laser scanner 11 for writing an image to a photosensitive drum 12 is provided on the top of the printer main body 1. Print data sent from an external apparatus such as a personal computer is received by a controller 40 which controls the printer main body 1 and outputted to a laser scanner 11 as written image data.

A plurality of sheet feeding sections 30 a, 30 b, 30 c, 30 d capable of feeding different kinds of sheets are located in the uppermost stream of sheet conveyance. In the image forming apparatus 100 of this embodiment, the sheet feeding sections 30 a to 30 d are provided in line vertically in the bottom portion of the apparatus. The sheet feeding sections 30 a, 30 b, 30 c, 30 d include feeding trays A, B, C, D for stacking and storing the sheets S and feeding portions 31 a, 31 b, 31 c, 31 d which separate the sheets S stored in the feeding tray and feed them.

The feeding portion 31 a (because the feeding portions 31 b, 31 c, 31 d have substantially the same structure as the feeding portion 31 a, description of those is omitted) includes a pickup roller 50 for picking up a sheet S in the feeding tray A, a feeding roller 51 for feeding the sheet S picked up by the pickup roller 50 and a separation roller 52 which opposes the feeding roller 51 for separating the sheets S by giving a separation force in a return direction to the sheet.

A conveyance roller pair 36 a (36 b, 36 c, 36 d) which takes over the sheet S fed by the feeding roller 51 and after conveyance by the feeding roller 51 ends, pulls out the sheet from nipping between the feeding roller 51 and the separation roller 52 are provided in the downstream of the feeding roller 51.

The conveyance roller pair 36 a has a role of taking over the sheet S conveyed through a longitudinal conveyance path 35 from a feeding section (for example, sheet feeding section 30 d) located further in the upstream in addition to this pulling action.

FIG. 7 is a block diagram of the control portion according to an embodiment. As shown in FIG. 7, an accumulation counter 40 a for measuring the quantity of fed sheets is incorporated in the controller 40. The accumulation counter 40 a counts the quantity of fed sheets from each feeding tray in cooperation with a feeding action signal and its count value is stored in a memory 40 b.

A resist roller pair 81 is provided at the lowermost stream position of the longitudinal conveyance path 35. This resist roller pair 81 executes the final skew correction of the sheet and matching of timing between image writing and sheet conveyance in the image forming portion.

The printer main body 1 includes a photosensitive drum 12, charger 13, laser scanner 11, development portion 14, transfer roller 19 and cleaner 26. The charger 13 charges the surface of the photosensitive drum 12 equally. The laser scanner 11 forms an electrostatic latent image by irradiating light to the surface of the photosensitive drum 12 charged by the charger 13. The development portion 14 develops the electrostatic latent image as a toner image with developing agent. The transfer roller 19 transfers a developed toner image to the sheet S. The cleaner 26 removes toner left in the photosensitive drum 12 after the toner image is transferred.

A conveying portion 21 for conveying the sheet S after the toner image is transferred and a fixing portion 22 for fixing an image on the sheet S conveyed by this conveying portion 21 as a permanent image are provided in the downstream of the image forming portion.

A discharge roller 24 for discharging the sheet S after the image is fixed by the fixing portion 22 from the printer main body 1 is provided. A discharged sheet stacking tray 25 which receives sheets S discharged by the discharge roller 24 is provided outside the top portion of the printer main body 1.

(Usage Frequency Equalizing Method)

Next, a method of equalizing the usage frequency as much as possible by reducing a difference of the usage frequency among the plurality of the sheet feeding sections of this embodiment will be described.

The pickup roller 50, the feeding roller 51 and the separation roller 52 equipped on the feeding portion 31 included in the sheet feeding section are worn (wasted) gradually with feeding of the sheets as described above. The wearing of the feeding roller 51 and the separation roller 52 is large because the load upon feeding is large and they need to be replaced several times until the service life of the image forming apparatus is fulfilled.

When any particular feeding portion of the plurality of the feeding portions is used unevenly at a high frequency, only the roller of that feeding portion is deteriorated early so that the service life for replacement is reached early and the replacement timings of the plural feeding portions become uneven. As a result, the number of maintenance for replacement of the roller increases or troubles such as jam or double feeding may occur because partial feeding portions are operated in a condition requiring maintenance in a long period.

Thus, in the image forming apparatus of the present invention, the controller 40 is provided with a function for equalizing the usage frequency of each feeding tray as much as possible.

As described above, the controller 40 is provided with the accumulation counter 40 a for counting the quantity of sheets fed from each feeding tray and the accumulation quantity of the sheets fed from each feeding tray is measured and the measured value is stored in the memory 40 b of the controller 40. Further, the controller 40 is also provided with a reservation counter 40 c for calculating a recent usage frequency of each sheet feeding sections in a predetermined period up to currently. This reservation counter 40 c measures the quantity of sheets fed in a specified period back with respect to currently and its value is always recorded in the memory 40 b of the controller 40. That is, this value is used as a recent usage frequency of the sheets set in each feeding tray.

In how long a period the usage frequency is to be measured with respect to currently may be changed depending on the apparatus usage condition of user and according to this embodiment, this period is set to a week by presuming the use condition of ordinary office.

As other function, the controller 40 has a bias detecting function for determining whether or not the use condition of each feeding tray is biased and a frequency equalizing function which when it is determined that the use condition is biased, estimates a sheet allocation to each feeding tray which can relax the bias.

Next, the above-described equalizing processing will be described specifically below. FIG. 1 shows a schematic flow chart of this frequency equalizing processing. In the meantime, the processing below can be executed in viewpoints of both hardware and software by the controller 40 as an estimating means in which a well known arithmetic operating means (CPU) 40 d and memory means (memory) 40 b are combined.

When the bias detecting processing is started by a timer in each predetermined period in step S1 as shown in FIG. 1, the controller 40 refers to the value of the accumulation quantity of fed sheets by each sheet feeding sections measured by the accumulation counter 40 a.

Next, the procedure proceeds to step S2, in which a difference DIF between a value Cmax of a sheet feeding section whose accumulation quantity of fed sheets is maximum and a value Cmin of a sheet feeding section whose accumulation quantity of fed sheets is minimum is compared with a set threshold TH. In the meantime, according to this embodiment, the threshold TH is set to 30,000.

Unless the difference DIF exceeds the threshold TH (No in S2), it is determined that the usage frequency of each sheet feeding sections is not so biased and then, the bias detecting processing is ended.

On the other hand, when the difference DIF is over the threshold TH (Yes in S2), the procedure proceeds to step S3, in which the values measured by the reservation counter 40 c are referred to about those two feeding trays. After that, the procedure proceeds to step S4, in which a recent usage frequency is compared.

When the recent usage frequency F1 of the sheet feeding section whose accumulation quantity of fed sheets is minimum is lower than the recent usage frequency F2 of the sheet feeding section whose accumulation quantity of fed sheets is maximum (Yes), the procedure proceeds to step S5. Then, it is determined that the bias of the usage frequency of the both feeding trays may not be improved in future and an alarm signal is outputted in step S5. when the usage frequencies of the both are in an opposite relation (No), the difference of the accumulation quantity of fed sheets can be relaxed by a future print operation, so that no alarm signal is outputted and then, the processing is ended.

In the present invention, the usage frequency means the frequency at which the sheet feeding section feeds the sheet. For example, the usage frequency can be expressed as the quantity of sheets fed per a portion time. The degree of wearing of the feeding roller, separation pad and the like can be estimated with such a usage frequency to some extent.

The frequency equalizing processing is triggered when the alarm signal is outputted in the bias detecting processing (step S6).

In a processing of this embodiment, the controller 40 introduces a sheet type preferred to be used in each feeding tray according to the accumulation quantity of fed sheets C by each sheet feeding sections measured by the accumulation counter 40 a and the recent usage frequency F of each sheet feeding sections (or type of sheet set in each feeding tray) measured by the reservation counter. when there exist a plurality of feeding trays for feeding the same kind of sheets, the controller 40 finds out which feeding tray should be used with preference.

The types of sheets to be used in each feeding tray are allocated to the feeding trays whose accumulation quantity of fed sheets is small with preference in order from sheet of material and size having the highest usage frequency currently. As a consequence, allocation of the type of the sheet recommended to be used in each feeding tray is determined so that the difference in usage frequency among the plurality of the sheet feeding sections can be reduced by a following sheet feeding operation.

Next, a specific processing flow will be described assuming a condition in which these functions operate actually. The image forming apparatus of this embodiment can execute a scheduled operation using a timer and thus, bias check of the usage condition of each sheet feeding sections by the bias detecting processing is automatically executed at a predetermined time once a week.

The controller 40 outputs an instruction for the bias detecting processing of determining whether or not there exists a bias in the usage frequency of each feeding tray. Assume that when this instruction is dispatched, the profile of each feeding tray is as shown in FIG. 2. At this time, the difference DIF between the value Cmax (43057) of a feeding tray A whose accumulation quantity of fed sheets is maximum and the value Cmin (12502) of a feeding tray D whose accumulation quantity of fed sheets is minimum is 30555. As described above, because the threshold TH for the bias determination is set to 30000 according to this embodiment, this difference DIF is over the threshold TH.

Because as a result of comparing the recent usage frequencies of sheets set in the both feeding trays, the feeding tray A (F2=1509/week) is used more frequently than the feeding tray D (F1=109/week), the alarm signal is outputted (step S5).

When the alarm signal is outputted, the frequency equalizing processing is started (step S6). The result of an ideal allocation of the sheet type in each feeding tray obtained in the above-described processing is outputted to eliminate the bias of the usage frequency in a future image forming operation (step S7).

The profile after the reallocation of the sheet types used in each feeding tray is as shown in FIG. 3 according to this embodiment. This output result is displayed on a display portion as a notifying means for notifying user of the sheet allocation. In the meantime, the notifying means of this embodiment may adopt a structure four notifying user with voice or blinking of a light emission device as well as the display portion such as the display portion described later.

A message recommending to change the allocation condition of the sheet types in each feeding tray to the profile shown in FIG. 3 is displayed on the display portion 3 of the image forming apparatus 100 (step S8). A thick paper A3 whose accumulation quantity of fed sheets is the smallest is set in the feeding tray A whose accumulation quantity of the fed sheets is the largest and a plain paper A3 whose accumulation quantity of the fed sheets is next to the smallest is set in the feeding tray C whose quantity of the fed sheets is next to the largest.

Although the feeding tray B has a next largest quantity, the plain paper A4 whose accumulation quantity of the fed sheets is the largest is set in the feeding tray B having a low usage frequency currently because the feeding tray D has a higher usage frequency currently. In this manner, user changes the allocation of the sheets to the feeding trays according to such an instruction. That is, as shown in FIG. 3, the feeding trays are replaced so that the sheets of the types allocated to each feeding tray are stored therein (step S9). As a result, the difference in the quantity of the accumulation quantity of the fed sheets among the sheet feeding sections is eliminated gradually through a following print operation.

As already described in this embodiment, the bias of the accumulation quantity of fed sheets among the respective sheet feeding sections can be suppressed to a specific range by checking periodically with the bias detecting processing, so that the difference in the usage frequency among the plural sheet feeding sections can be reduced.

Next, processing of this embodiment in case where the sheet materials of the same kind and size are set in a plurality of the feeding trays will be described. In the image forming apparatus of this embodiment, a preference order for use is allocated to the plurality of the feeding trays in which the same sheets are set and when there are left sheets in a feeding tray having a higher preference order, they are fed first of all necessarily.

Assume that when an instruction for the bias detecting processing is dispatched, the profile of the respective feeding trays is as shown in FIG. 4. At this time, a difference between the value Cmax (44160) of the feeding tray A whose accumulation quantity of fed sheets is maximum and the value Cmin (13022) of the feeding tray C whose accumulation quantity of fed sheets is minimum is 31138. Because the bias determination threshold TH of this embodiment is set to 30000, it comes that the value of this difference DIF is over the threshold TH.

Because the feeding tray A (F2=1612/week) is used more frequently than the feeding tray C (F1=109/week) when the recent usage frequencies of sheets set in both the feeding trays are compared, an alarm signal is outputted in step S5.

When the alarm signal is outputted, the procedure proceeds to step S6, in which the frequency equalizing processing is started. An estimation result of the ideal allocation of the sheet type used in each feeding tray obtained in the previously described processing is outputted to eliminate the bias of the usage frequency in the image forming operation in the future naturally (S7). In this case, the profile after the types of the sheets used in each feeding tray are reallocated is as shown in FIG. 5. At this time, a higher selection preference order is automatically allocated to two feeding trays in which the plain papers of A4 size of the same kind are set in the order from a feeding tray to which the sheets are reallocated whose accumulation quantity of fed sheets is smaller.

A message which recommends user to change the allocation condition of sheets to each feeding tray to this profile is displayed on the display portion 3 of the image forming apparatus 100 (step S8). The procedure proceeds to step S9, in which user inputs a setting change to the display portion 3 and then, the procedure proceeds to step S10, in which the types of the sheets to be set in each feeding tray are replaced by the user actually. As a consequence, the controller 40 recognizes the sheets of the types indicated on the display portion through a detecting means for detecting that they are loaded on the respective sheet feeding sections and this preference order is applied. Consequently, an error of replacement of the plural sheet types can be reduced by provision of such a detecting means. Then, the procedure proceeds to step S11, in which the values of the reservation counter are replaced corresponding to the feeding trays which replace the sheet types.

In the meantime, the present invention is not restricted to the above-described embodiments. Although this embodiment adopts a structure of executing the bias detecting processing periodically by schedule control, this bias detecting processing may be executed necessarily within a predetermined time after the apparatus main body is powered on.

In addition, difference in accumulation quantity of fed sheets is always counted for each print job, then the above-described processing may be executed when the difference exceeds the threshold.

The above-described processing may be executed each time when the accumulation quantity of fed sheets to the apparatus main body reaches a predetermined number instead of the accumulation quantity of the fed sheets by the sheet feeding section. For example, that processing may be executed each time when the accumulation quantity of the fed sheets to the apparatus main body reaches 100,000.

Information of each sheet feeding sections for which the sheet allocation is changed may be transmitted to outside through communication means. Such a structure enables the usage frequency of each sheet feeding sections to be notified to an outside service center or the like, thereby making it possible to estimate a replacement timing of the roller or separation pad to lead to effective maintenance.

The trigger of the bias detecting processing may be executed according to an instruction from outside by user or according to an instruction through remote control from an outside service station connected through communication line. With such a structure, the usage frequency of a sheet feeding sections having a high usage frequency can be reduced according to an instruction from outside even when the feeding components of part of the sheet feeding section are worn so that jam is likely to occur. Therefore, conveyance trouble before maintenance can be reduced.

In this embodiment, the reallocation processing of equalizing the degree of wearing of members used in each feeding tray is carried out by rearrangement of the feeding trays using comparison of difference of the accumulation quantity of fed sheets by the accumulation counter and the recent usage frequency by the reservation counter. However, the present invention is not restricted to this processing algorithm. That is, when higher arithmetic operating processing can be executed on the controller side, more effective equalization is possible by recording history of previous size changes and the trend of the usage frequency of each sheet type and using such information for processing.

Because a conveyance distance required for conveying a sheet varies depending on the sheet size, the above processing may be carried out corresponding to not only the quantity of sheets but also an accumulated conveyance distance (=quantity of fed sheets×paper size). As a consequence, the degree of wearing of the feeding members such as the pickup roller, feeding roller and separation roller can be more equalized in each sheet feeding member. Thus, the component replacement timing of each sheet feeding sections can be aligned thereby achieving effectiveness of maintenance.

In the description of this embodiment, it is described that the sheets in each feeding tray are replaced. However, when the sheet storage portion of the feeding trays A to D can be removed from the printer main body 1 and replaced with each other, the types of the sheets preferred to be fed by each sheet feeding sections may be replaced by replacing the sheet positions together with the feeding trays.

As described above, according to the present invention, the difference of the usage frequency of the respective sheet feeding sections can be reduced not only among the plural sheet feeding sections loaded with the same type of sheets but also among the plural sheet feeding sections loaded with different type of sheets, which cannot be achieved conventionally.

As a consequence, such replaceable members as the feeding roller and separation roller included in particular sheet feeding sections can be prevented from being worn unevenly in a short period or being kept not used in a long period, thereby reducing the occurrence frequency of trouble such as jamming or double feeding.

Further, because all the feeding rollers and separation rollers can be used in a same pace, maintenance interval for component replacement by a service person can be expanded to its maximum extent. Further, because the consumption parts of all the sheet feeding sections can be replaced in a single maintenance at the same time, the frequency of visits by the service person can be reduced largely.

This application claims priority from Japanese Patent Application No. 2005-191408 filed Jun. 30, 2005, which is hereby incorporated by reference, herein. 

1. An image forming apparatus comprising: a plurality of sheet feeding sections capable of feeding different types of sheets; an image forming portion which forms an image on a sheet fed by the sheet feeding sections; an accumulation feeding quantity counting means capable of counting the accumulation quantity of fed sheets of each of the plural sheet feeding sections; and a control means which determines the bias of usage frequency of each sheet feeding sections based on a counting result of the accumulation feeding quantity counting means and changes the allocation of the sheets of each sheet feeding sections so as to reduce the bias of the usage frequency of each sheet feeding sections.
 2. The image forming apparatus according to claim 1, wherein the control means, when a difference between accumulation quantity of fed sheets of any two sheet feeding sections of the plural sheet feeding sections is larger than a predetermined value, changes the allocation of the sheet based on a count result of the accumulation feeding quantity counting means and when the difference of the accumulation quantity of the fed sheets is smaller than the predetermined value, does not change the allocation of the sheet.
 3. The image forming apparatus according to claim 2, wherein an alarm signal is outputted when the allocation of the sheets by the control means is necessary.
 4. The image forming apparatus according to claim 1 further comprising: a usage frequency calculating means for calculating the usage frequency of each of the plural sheet feeding sections in a predetermined period up to currently, wherein when a difference between accumulated quantities of fed sheets of any two sheet feeding sections of the plural sheet feeding sections is over a predetermined value and the usage frequency of a sheet feeding section, whose accumulation quantity of fed sheets is smaller of the two sheet feeding section, is lower than the usage frequency of the other sheet feeding section, whose accumulation quantity of fed sheets is larger of the two sheet feeding sections, based on a counting result of the accumulation feeding quantity counting means and a calculation result of the usage frequency calculating means, the control means changes the allocation of the sheets.
 5. The image forming apparatus according to claim 4, wherein an alarm signal is outputted when the allocation of sheets by the control means is necessary.
 6. The image forming apparatus according to claim 1, further comprising a notifying means for notifying the allocation of sheets changed by the control means.
 7. The image forming apparatus according to claim 6, wherein the notifying means is capable of transmitting a result of sheet allocation to an external device through communication means.
 8. The image forming apparatus according to claim 1, wherein when the types of sheets set in the sheet feeding sections are equal in two or more sheet feeding sections, sheets are allocated to use the sheet feeding sections whose accumulation quantity of fed sheets is smaller with preference.
 9. The image forming apparatus according to claim 1, wherein determination of bias of the usage frequency of each sheet feeding sections by the control means is started in each predetermined period.
 10. The image forming apparatus according to claim 1, wherein the determination of bias of the usage frequency of each sheet feeding sections by the control means is started in each predetermined period after the power of the apparatus main body is turned on.
 11. The image forming apparatus according to claim 1, wherein the determination of bias of the usage frequency of each sheet feeding sections by the estimation means is started each time when the accumulation quantity of fed sheets to the apparatus main body reaches a predetermined one.
 12. The image forming apparatus according to claim 1, wherein the determination of bias of the usage frequency of each sheet feeding sections by the estimating means is started according to an instruction from outside through a receiving means. 